The BSA maintains a sewer collection system of approximately 850 miles in length with 10 outlying pump stations and a 17 million gallon capacity storm retention basin. The collection system conveys on average nearly 150 million gallons per day (MGD) to the Bird Island Wastewater Treatment Plant (WWTP), including more than 30 million gallons per day from outside municipalities tributary to the BSA system. Aside from the City of Buffalo proper, the BSA collection serves in part or in total the Towns of Alden, Cheektowaga, Elma, Lancaster, Tonawanda, and West Seneca and the Villages of Depew, Lancaster and Sloan as well as Erie County Sewer District Numbers 1 and 4.
The BSA collection system currently consists of a mix of Separate Sanitary Sewer Systems (SSS), Separate Storm Sewers, and Combined Sewer Systems (CSS). Again these systems combined include more than 850 miles of pipe, of which the majority (790 miles) are combined. The Combined Sewer System (CSS) was designed and constructed to convey sanitary sewage and stormwater in a single pipe system to the WWTP. Currently the combined system has the capacity to transmit up to 560 MGD of wastewater to the WWTP. The 560 MGD flow equates to roughly 85% of the volume of stormwater and sanitary sewage generated within the entire service area.
As discussed, the majority of the BSA’s system is combined in that both sanitary and stormwater are collected within a single network of pipes. By comparison, portions of the City as well as all tributary municipalities are served by separate systems where sanitary and stormwater is collected within two distinct piping systems. The combined system was the preferred method of collection for many similar era cities. Today roughly 43 million people in 1,100 communities across the United States are served by combined systems.
While the Bird Island WWTP is designed to treat upwards of 560 MGD of flow, the actual amount of water (storm and sanitary) collected within the combined system at times exceeds that amount. As such and as a means of protecting the treatment plant and private property from flooding, including basements, the system was designed and constructed with a number of Combined Sewer Overflow (CSO) points. CSOs are designed discharge points which release untreated wastewater to local receiving streams when the capacity of the CSS is exceeded during wet weather. In total the BSA system was constructed with a total of 65 CSOs. Over time and in response to regulatory pressure, the BSA has reduced this number to 59 CSOs.
Flow within the combined system is controlled by numerous regulators (referred to as sewer patrol points (SPPs) in the BSA system), which essentially maintain the dry weather flow and a portion of the wet weather flow within the collection system (for conveyance to the WWTP) and allows for discharge of wet weather flows in excess of the CSS capacity. Within the BSA system, these SPPs consist of fixed weirs. In total there are currently 258 SPPs in the BSA system.